Technological advances aren't always kind to Mother Earth — witness the impact of nuclear waste, industrial emissions and plastic bottles — but high-tech environmental monitoring systems are also helping us get a handle on the state of our planet. It's good to remember that as Earth Week draws to a close.

Just in the past couple of years, NASA has added to the nation's fleet of Earth-observing satellites. In 2011, the $1.5 billion Suomi NPP satellite went into orbit, blazing a trail for a new generation of planet-watchers that can provide data about extreme weather as well as environmental indicators. Suomi's five sensor systems are tracking atmospheric and sea surface temperatures, biological productivity, ozone levels and much, much more.

This February, the $855 million Landsat Data Continuity Mission finally got off the ground, opening a new chapter for the 41-year-old Landsat Earth-monitoring program. LDCM will monitor surface temperatures around the planet and generate 400 images a day in visible and infrared wavelengths. Multi-wavelength observation is a key technology for monitoring the planet's health, because thermal infrared readings can tell you how vegetation is faring, how much heat the world's cities are putting out, and how the world is coping with climate change.

Even Earth's gravity field can provide insights into how the planet is changing: Readings from the Gravity Recovery and Climate Experiment, or GRACE, have traced the loss of ice from the world's glaciers and ice caps by measuring subtle changes in our planet's distribution of mass. "It's really a phenomenal source of information to study water on the surface," Tucker said.

For decades, observations from outer space — including data from NASA satellites such as Terra and Aqua, as well as the National Oceanic and Atmospheric Administration's weather satellites and the Landsat constellation — have been helping scientists understand what's happening to our environment.

Suomi NPP and LDCM are continuing that legacy, but there are still concerns about the future: Last year, the National Research Council voiced grave concerns about America's aging Earth-observing system, saying that the projected loss of satellite capability "will have profound consequences on science and society, from weather forecasting to responding to natural hazards."